Purification of alkyl naphthalenes by distillation and furfural extraction

ABSTRACT

Methylnaphthalenes are obtained from a hydrocarbon mixture boiling within the range of 375* to 600*F containing alkylnaphthalenes and non-naphthalenes by distilling the hydrocarbon mixture to a boiling range of 460*-530*F and then treating this narrow boiling range fraction with a furfural extraction.

United States Patent [191 Cherry et al.

[ PURIFICATION OF ALKYL NAPHTHALENES BY DISTILLATION AND F URFURAL EXTRACTION [75] Inventors: Wesley R. Cherry, Prospect Park,

DeL; Kenneth A. Scott, Swarthmore, Pa.

[73] Assignee: Sun Ventures, lne., St. Davids, Pa. [22 l'iledz Dec. 26, 1973 1211 Appl. N11; 428,285

Related US. Application Data [63] Continuation of Ser. No. 2l4,3l7, Dec. 30. 1971,

[58] Field of Search 260/674 N, 674 SE, 674 A 203/43, 68-70, 62, 58

[ Mar. 4, 1975 3,082,270 3/1963 McKennis 260/674 N 3,168,463 2/1965 Norton @1211. ..260/674N 3,172,919

3/1965 Hagerty et al. 260/674 N Primary E.\'anu'ner-Wilbur L. Bascomb. Jr. Attorney, Agent, or Firm-George L. Church; J. Edward Hess; Donald R. Johnson 571 ABSTRACT Methylnaphthalenes are obtained from a hydrocarbon mixture boiling within the range of 375 to 600F c0ntaining alkylnaphthalenes and non-naphthalenes by distilling the hydrocarbon mixture to a boiling range of 460-530F and then treating this narrow boiling range fraction with a furfural extraction.

[56] References Cited UNITED STATES PATENTS 8 Claims ZDraWmg Fgures 2.7271354 12/1955- Brown et al. 260/674 N JILCAAQ PI/MAR 1 .3 9 aeg o mmy x ,v E ffiyr-kao'fl) 1 p/s'r/zggr/av Flu/1w 62MB. f7 nae 2m:

I. "I new rnv 6/ meta: M 4 220 (460 F, H3022 mgnvrgg 3Q LQEEQZC Cmvrggrgg man/04g IJ M6142 m ML /4 gar/wag Mimi/g fi/flfl BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a method of separating al-' kylnaphthalenes from a hydrocarbon feed comprising alkylnaphthalenes and non-naphthalenes.

2. Description of the Prior Art It is known that naphthalenic compounds, for example, polycyclic aromatic compounds such as the alkylnaphthalenes, are present in certain fractions derived from petroleum. Specifically, petroleum fractions which boil within the range of 375 to 600F. generally contain substantial amounts of alkylnaphthalenes, such as mono-, di-, and tri-methylnaphthalenes and in smaller quantity, the ethylnaphthalenes. Recycle fractions, which are formed in the cracking of petroleum stocks and which include this boiling range, often contain major proportions of aromatic hydrocarbons that are mainly alkylnaphthalenes. Also present in significant quantities are the non-naphthalenes like the monocyclic aromatic hydrocarbons i.e. having one aromatic ring such as the alkyl benzenes, tetralin, indan, indene and their alkyl derivatives; certain tricyclicaro- 'naphthalenes including monocyclic aromatics, tricyclic matic hydrocarbons, i.e. having three aromatic rings and non-aromatic hydrocarbons. Isolating these aromatic hydrocarbons from each other and from the aliphatic hydrocarbons is a difficult and complicated process. The separation is usually performed through selective solvent extraction.

Solvent extraction is a well known process for the separation of aromatic hydrocarbons from mixtures with nonaromatic hydrocarbons of similar boiling range. Furfural has been found to be an excellent selective solvent in the separation of hydrocarbons of relatively high boiling point, for example, hydrocarbons useful in the manufacture of lubricating oils and catalytic cracking feed stocks. Furfural extraction has also been found useful in the preparation of alkylnaphthalene concentrates as disclosed in commonly assigned U.S. Pat. No. 3,172,919 issued to Peter Frank Hagerty, Harold Foo-Heng Tse and Harland Jay Surrena issued Mar. 9, I965. According to this process a fraction derived from cracked gas oil and boiling mainly in the range 440-515F. is extracted with furfural and followed by re-extraction of the furfural layer with a saturated hydrocarbon. In general, however, such alkylnaphthalene concentrates contain compounds whose boiling points are so close to those of the methylnaphthalene isomers that methylnaphthalenes having purities higher than 95 percent, cannot be attained using this method even when the extract is redistilled. These methylnaphthalene's particularly the dimethylnaphthalenes are highly desirable articles of commerce in that they are intermediates for polyester resins which have outstandingly good properties for fiber applications.

SUMMARY OF THE INVENTION We have now discovered an economical process whereby mcthylnaphthalenes are obtained from a hydrocarbon mixture boiling within the range of 375 to 6()()F comprising alkylnaphthalenes including methylnaphthalene and dimethylnaphthalene, and nonaromatics and non-aromatics which comprises:

a. distilling said hydrocarbon feed in a distillation zone and withdrawing from said distillation zone a hydrocarbon fraction boiling mainly in the range of 460530F; countercurrently extracting said hydrocarbon boiling mainly in the range of.460530F. and comprising alkylnaphthalenes including methylnaphthalene and dimethylnaphthalene, monocyclic aromatics and nonaromatics with furfural solvent at a temperature in the range of l0-l 50F, the ratio of solvent to the total aromatics in the charge fraction being in the range of 0.75:1 to 7:1 on a volume basis;

. separating an extract phase from a rafftnate phase;

. countercurrently contacting the extract phase at a temperature in the range of 10-150F. with saturated hydrocarbon of the C -C range in amount of 0.5 to 2.0 volumes of said saturated hydrocarbon per volume of extract in the extract phase, whereby said saturated hydrocarbon mainly dissolves in the diluted extract'phase and displaces therefrom nonaromatic and a minor amount of the monocyclic aromatics to form a reject phase containing said displaced non-aromatics and monocyclic aromatics and only a minor proportion of said saturated hydrocarbon;

. removing the reject phase;

. removing a furfural phase containing most of the alkylnaphthalenes and most of the C -C,, saturated hydrocarbon; and

g. separating mono and dimethylnaphthalene concentrate from said furfural phase.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic flowsheet of one embodiment of the invention.

FIG. 2 is a schematic flowsheet of a modification of the extraction step in the process.

A more detailed description will be found hereinbelow.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In general, the substituted condensed ring dicyclic aroleast economically advantageous amounts of alkylnaphthalenic compounds. However, hydrocarbons feeds having alkylnaphthalene contents over 25 percent are preferred.

According to the invention the above described hydrocarbon feed is placed in a distillation zone and a hydrocarbon fraction boiling mainly in the range of 460-530F but preferably boiling mainly in the range of 480520F is withdrawn. lf monoand dimethylnaphthalenes are desired the 460530F fraction is used. 1f dimethylnaphthalene is desired then the narrower fraction should be used. The desired hydrocarbon fraction is first countercurrently extracted with a furfural solvent in limited amount but sufficient to extract essentially all of the dicyclic aromatics. Most of the non-aromatics and a portion of the monocyclic aromatics remain in the raffinate phase and are removed. The extract phase contains essentially all of the dicyclic aromatics, a major part of the monocyclic aromatics and also a substantial but minor amount of the nonaromatics. The extract phase is then treated with a C,-,C,, saturated hydrocarbon, such as hexane or isooctane, in a manner whereby essentially all of the non-- aromatics and a portion of the monocyclic aromatics are displaced therefrom, being replaced by the C -C saturated hydrocarbon. In some cases, prior to such treatment it may be necessary that the extract phase be diluted with more furfural solvent within a limited proportion range as hereinafter specified. Omissioh of this dilution step can vitiate the treatment with the C C saturated hydrocarbon and result in failure in achieve the desired displacement of the non-aromatics. Then treating with hexane or isooctane in the proper amount, product can be obtained which contains nearly all of the methylnaphthalenes and essentially none of the non-aromatics that were present in the feed.

Referring first to FIG. 1, a hydrocarbon fraction boiling in the range 375600F derived from catalytic gas oil having an alkylnaphthalene content of 48.5 percent by weight and a non-naphthalene content including alkylbenzenes, monocyclic aromatics and non-aromatics of 51.5 percent by weight is introduced through line 1 into distillation column 2 wherein a conventional distillation operation is performed. An overhead fraction boiling 460F and lighter is withdrawn through line 3 to storage or further processing. A bottom fraction boiling 530F and heavier is withdrawn through line 4 to storage or further processing. A side stream fraction being in the range of 460520F is withdrawn through line 5 and introduced into cooler 6. The cooled fraction is withdrawn through line 7 and is introduced into the bottom of a countercurrent extractor 8. Furfural solvent, herein referred to as primary furfural is introduced to the top of the column through line 9 and flows downwardly therein countercurrent to the feed. The term furfural solvent as used herein refers to furfural itself of furfural containing dissolved water in any amount up to saturation at the temperature of the extraction operation. Column 8 should be operated at a temperature in the range of 10l 50F., and more preferably 701 10F. In this operation it is important that the amount of primary furfural feed to the column be such that, on a volume basis, its ratio to the total aromatics in the feed lies in the range of 0.75:1 to 7:1 and more preferably 1:1 to 2:1. Under these conditions the extract phase, which is withdrawn from the column through line 10 and is herein referred to as the 1st extract phase," will contain essentially all of the dicyclic aromatics, while the raffinate phase, which is removed via line 11, will contain a major proportion of the nonaromatics and some of the monocyclic aromatics.

The 1st extract phase in line 10 when necessary is admixed with an appropriate amount of additional furfural solvent, herein referred to as "secondary furfural, fed through'line l2, and the mixture is sent to the top of a second column 13. It is important that the amount of secondary furfural used be in the range ofO. 15 to 2.5 volumes per volume of extract (i.e., gas oil hydrocarbons) in the extract phase and more preferably in the range of 0.25 to 1.25 volts/vol.

A C -C saturated hydrocarbon or narrow-boiling range mixture of such hydrocarbons is feed to the bot tom of column 13 through line 14 and therein passes upwardly in contact with the downflowing extract phase. Any paraffinic or naphthenic C -C hydrocarbon or narrow-boiling range mixture thereof can be used for this purpose. The C -C hydrocarbon material can contain a minor amount, for example, up to 10% by volume of aromatic components such as benzene and toluene. 1n the present description iso-octane will be condsidered as the saturated hydrocarbon employed. Again, it is important that the amount of isooctane be regulated within a specific range, namely, from 0.5 to 2.0 vol. per vol. of extract in theh 1st extract phase fed to the top of column 13. More preferably, this ratio is in the range of 0.751.1 vols/vol. The temperature of this operation can be in the range of 10-150F., more preferably -1l0F., and it most preferably is about the same as the temperature used for the extraction in column 8. Contact of the isooctane in the amount specified with the 1st extract phase causes most of the iso-octane to dissolve in the furfural and displace the non-aromatics. There is withdrawn from the top of the column through line 15 a reject phase which contains essentially all of the nonaromatics that were present in the 1st extract phase and only a small amount of the iso-octane used. From the base of the column a 2nd extract phase is removed through line 16. This material contains nearly all of the methylnaphthalenes.

FIG. 2 illustrates a modification of the process in which the first column (not shown) is operated in the same manner as described above but the second column 20 is operated with a stripping section at the top. The secondary furfural from line 21 is split into two streams with part flowing to the top of the column and the remainder being introduced through line 22 into the 1st extract phase which passes through line 23 to an intermediate level in column 20. lsooctane is fed to the bottom through line 25. The amount of furfural introduced through line 22 should be at least 15% by volume based on the extract in the 1st extract phase. The portion of the column above line 23 contstitutes a stripping section in which the reject phase is countercurrently contacted with the remainder of the secondary furfural. This type of operation tends to give a still higher recovery of methylnaphthalenes aromatic in the 2nd extract phase removed from the base of the column through line 24. The reject'phase is removed through line 26.

In practicing either of the above-described embodiments, it is preferred to use furfural solvent which contains water and more preferably which is substantially saturated with water at the temperature of operation. lt has been found that the presence of water in the solvent lowers its capacity for monocyclic aromatics while leaving the capacity for dicyclic aromatics substantially unaffected. Hence the use of water in the primary and secondary furfural results in obtaining a dicyclic aromatic concentrate of higher purity without reducing the recovery of dicyclic aromatics.

TABLE I By way of comparison from the data above it-can be seen that the full boiling range material was not improved even with repeated furfural extractions. Note that beyond the fourth extraction the full boiling range material still contained 842% ofthe non-miphthalenie impurities while the narrower range was improved to 98% dimethylnaphthalenes in four extractions.

We claim:

COMPARISON EXTRACTION 71'NONNAPHTHALENES METHYLNAPHTHALENES belled Furfural Extract No. 1. Each furfural extract was then mixed with 1 volume of iso-octane and allowed to separate into two layers, whereupon the iso-octane layer was removed. After a total of three such isooctane extractions, the hydrocarbons in the furfural layer were found to have the analyses shown in line 3 of Table l. labelled Furfural Extract No. 4.

The surprising and beneficial results of close fractionation before extraction can be seen by comparing the analyses of the furfural extracts of the starting materials. ln spite ofthe fact that the close-fractionated starting material actually had a slightly lower methylnaphthalene content than did the full-boiling range ma terial. the furfural extracts of the close-fractionated material had a significantly higher methylnaphthalene content.

Another beneficial effect of the present process is that it enhances the efficiency of the extraction step. To show this effect the following data are presented in the following Table II.

1. Process for separating mono and dimethylnaphthalene from a hydrocarbon feed comprising alkylnaphthalenes including methylnaphthalenes and dimethylnaphthalenes and non-naphthalenes including monocyclic hydrocarbons and non-aromatic hydrocarbons, said feed boiling in the range from 375600F. and containing 25-977z aromatics and over 25% alkylnaplr thalenes which comprises:

a. distilling said hydrocarbon feed in a distillation zone;

b. withdrawing from said distillation zone a hydrocarbon fraction boiling mainly in the range of 460-530F;

c. countercurrently extracting said hydrocarbon fraction boiling mainly in the range of 460-530F. comprising alkylnaphthalenes, monocyclic aromatics, tricyclic aromatics and non-aromatic hydrocarbons with furfural solvent at a temperature in the range of 10 to 150F., the ratio of furfural to the total aromatics in the charge fraction being in the range of 0.75:1 to 7:1 by volume;

d. separating an extract phase from a raffinate phase;

e. countercurrently contacting the extract phase at a temperature in the range of 10 to 150F. with saturated hydrocarbon of the C -C range in amount of 0.5 to 2.0 volumes of said saturated hydrocarbon per volume of extract in the extract phase. whereby said saturated hydrocarbon mainly dissolves in the diluted extract phase and displaces therefrom nonaromatic hydrocarbons and a minor amount of the monocyclic aromatics to form a reject phase containing displaced non-aromatics, monocyclic aromatics and only a minor proportion of said saturated hydrocarbon;

. removing the reject phase g. removing the furfural phase containing most of the mono and dimethyl naphthalenes and most of the C -C saturated hydrocarbon; and

. separating the mono and dimethylnaphthalene concentrate of higher than purity from said furfural phase.

2. Process according to claim I in which the extract phase in step (d) is diluted with furfural solvent in an amount of from 0.15 to 2.5 volumes of diluent solvent per volume of extract in the extract phase before step 3. Process according to claim 1 wherein said furfural solvent is furfural substantially saturated with water.

4. Process according to claim 1 wherein said saturated hydrocarbon is isooctane.

5. Process for separating dimethylnaphthalene from a hydrocarbon feed comprising alkylnaphthalenes including methyl naphthalenes and dimethylnaphthalenes and non-naphthalenes including monocyclic aromatic hydrocarbons, and non-aromatic hydrocarbons, said feed boiling in the range from 375600F. and containing 25-97% aromatics and over 25% alkylnaphthalenes which comprises;

a. distilling said hydrocarbon feed in a distillation zone;

b. withdrawing from said distillation zone a hydrocarbon fraction boiling mainly in the range of 480520F.,

c. countercurrently extracting said hydrocarbon fraction boiling mainly in the range of 480520F. comprising alkylnaphthalenes, monocyclic aromatics. tricyclic aromatics and non-aromatics hydrocarbons with furfural solvent at a temperature in the range of -150F., the ratio of furfural to the total aromatics in the charge fraction being in the range of 0.75:1 to 7:1 by volume,

01. separating an extract phase from a raffinate phase;

e. countercurrently contacting the extract phase at a temperature in the range of 10 to 150F. with saturated hydrocarbon of the C -C range in amount of 0.5 to 2.0 volumes of said saturated hydrocarbon per volume of extract in the extract phase, whereby said saturated hydrocarbon mainly dissolves in the diluted extract phase and displaces therefrom aliphatic hydrocarbons and a minor amount of the monocyclic aromatics to form a reject phase containing displaced non-aromatics monocyclic aromatics, and only a minor proportion of said saturated hydrocarbon;

f. removing the reject phase;

g. removing the furfural phase containing most of the 'dimethylnaphthalenes and most of the C -C satu rated hydrocarbon; and

h. separating dimethylnaphthalene of higher than purity from said furfural phase.

6. Process according to claim 5 in which the extract phase in step (d) is diluted with furfural solvent in an amount of from 0.15 to 2.5 volumes of diluent solvent per volume of extract in the extract phase before step (e).

7. Process according to claim 5 wherein said furfural solvent is furfural substantially saturated with water.

8. Process according to claim 5 wherein said saturated hydrocarbon is isooctane. 

1. PROCESS FOR SEPARATING MONO AND DIMETHYLNAPHTHALENE FROM A HYDROCARBON FEED COMPRISING ALKYLNAPHTHALENES INCLUDING METHYLNAPHTHALENES AND DIMETHYLNAPHTHALENES AND NON-NAPHTHALENES INCLUDING MONOCYCLIC HYDROCARBONS AND NON-AROMATIC HYDROCARBONS, SAID FEED BOILING IN THE RANGE FROM 375*-600*. AND CONTAINING 25-97% AROMATICS AND OVER 25% ALKYLNAPHTHALENES WHICH COMPRISES: A. DISTILLING SAID HYDROCARBON FEED IN A DISTILLATION ZONE, B. WITHDRAWING FROM SAID DISTILLATION ZONE A HYDROCARBON FRACTION BOILING MAINLY IN THE RANGE OF 460*-350*F, C. COUNTERCURRENTLY EXRACTING SAID HYDROCARBON FRACTION BOILING MAINLY IN THE RANGE OF 460*-530*F, COMPRISING ALKYLNAPHTHALENES, MONOCYCLIC AROMATICS, TRICYCLIC AROMATICS AND NON-AROMATIC HYDROCARBONS WITH FURFURAL SOLVENT AT A TEMPERATURE IN THE RANGE OF 10* TO 150*F., THE RATIO OF FURFURAL TO THE TOTAL AROMATICS IN THE CHARGE FRACTION BEING IN THE RANGE OF 0.75:1 TO 7:1 BY VOLUME, D. SEPARATING AN EXTRACT PHASE FROM A RAFFINATE PHASE, E. COUNTERCURRENTLY CONTACTING THE EXTRACT PHASE AT A TEMPERATURE IN THE RANGE OF 10 TO 150*F. WITH SATURATED HYDROCARBON OF THE C5-C8 RANGE IN AMOUNT OF 0.5 TO 2.0 VOLUMES OF SAID SATURATED HYDROCARBON PER VOLUME OF EXTRACT IN THE EXTRACT PHASE, WHEREBY SAID SATURATED HYDROCARBON MAINLY DISSOLVES IN THE DILUTED EXTRACT PHASE AND DISPLACES THEREFROM NON-AROMATIC HYDROCARBONS AND A MINOR AMOUNT OF THE MONOCYCLIC AROMATICS TO FORM A REJECT PHASE CONTAINING DISPLACED NON-AROMATICS, MONOCYCLIC AROMATICS AND ONLY A MINOR PROPORTION OF SAID SATURATED HYDROCARBON, F. REMOVING THE REJECT PHASE G. REMOVING THE FURFURAL PHASE CONTAINING MOST OF AND DIMETHYL NAPHTHALENES AND MOST OF THE C5-C8 SATURATED HYDROCARBON, AND H. SEPARATING THE MONO AND DIMETHYLNAPHTHALENE CONCENTRATE OF HIGHER THAN 95% PURITY FROM SAID FURFURAL PHASE.
 2. Process according to claim 1 in which the extract phase in step (d) is diluted with furfural solvent in an amount of from 0.15 to 2.5 volumes of diluent solvent per volume of extract in the extract phase before step (e).
 3. Process according to claim 1 wherein said furfural solvent is furfural substantially saturated with water.
 4. Process according to claim 1 wherein said saturated hydrocarbon is isooctane.
 5. Process for separating dimethylnaphthalene from a hydrocarbon feed comprising alkylnaphthalenes including methyl naphthalenes and dimethylnaphthalenes and non-naphthalenes including monocyclic aromatic hydrocarbons, and non-aromatic hydrocarbons, said feed boiling in the range from 375*-600*F. and containing 25-97% aromatics and over 25% alkylnaphthalenes which comprises; a. distilling said hydrocarbon feed in a distillation zone; b. withdrawing from said distillation zone a hydrocarbon fraction boiling mainly in the range of 480*-520*F., c. countercurrently extracting said hydrocarbon fraction boiling mainly in the range of 480*-520*F. comprising alkylnaphthalenes, monocyclic aromatics, tricyclic aromatics and non-aromatics hydrocarbons with furfural solvent at a temperature in the range of 10*-150*F., the ratio of furfural to the total aromatics in the charge fraction being in the range of 0.75:1 to 7:1 by volume, d. separating an extract phase from a raffinate phase; e. countercurrently contacting the extract phase at a temperature in the range of 10* to 150*F. with saturated hydrocarbon of the C5-C8 range in amount of 0.5 to 2.0 volumes of said saturated hydrocarbon per volume of extract in the extract phase, whereby said saturated hydrocarbon mainly dissolves in the diluted extract phase and displaces therefrom aliphatic hydrocarbons and a minor amount of the monocyclic aromatics to form a reject phase containing displaced non-aromatics monocyclic aromatics, and only a minor proportion of said saturated hydrocarbon; f. removing the reject phase; g. removing the furfural phase containing most of the dimethylnaphthalenes and most of the C5-C8 saturated hydrocarbon; and h. separating dimethylnaphthalene of higher than 95% purity from said furfural phase.
 6. Process according to claim 5 in which the extract phase in step (d) is diluted with furfural solvent in an amount of from 0.15 to 2.5 volumes of diluent solvent per volume of extract in the extract phase before step (e).
 7. Process according to claim 5 wherein said furfural solvent is furfural substantially saturated with water.
 8. Process according to claim 5 wherein said saturated hydrocarbon is isooctane. 